A total of 146,042 patients with mild psoriasis, 3,956 patients with severe psoriasis, and 766,950 patients without psoriasis were included in the analyses. Overall, psoriasis patients were older, contributed greater person-time, and had higher rates of depression, anxiety and suicidality occurring prior to cohort entry than patients without psoriasis (). Over half (57.74%) of severe psoriasis patients were treated with methotrexate ().
The unadjusted (crude) incidence of clinical diagnosis of depression, anxiety and suicidality in patients with psoriasis was 25.9, 20.9 and 0.9 per 1000 person years, respectively (data for mild and severe psoriasis groups shown separately in ). The hazard ratios (relative risks) for receiving a clinical diagnosis of depression, anxiety and suicidality after cohort entry in patients with psoriasis compared to controls, after adjusting for age and sex, were 1.39 (95% confidence interval [CI] 1.37, 1.41), 1.31 (95% CI 1.29, 1.34) and 1.44 (95% CI 1.32, 1.57), respectively. The adjusted relative risk of diagnosis of depression was higher in patients with severe psoriasis (HR 1.72, 95% CI 1.57, 1.88) than mild psoriasis (HR 1.38, 95% CI 1.35, 1.40) (). The adjusted relative risk of anxiety was similar in both mild and severe psoriasis groups compared to controls (). The adjusted HR of suicidality was higher in patients with severe psoriasis (HR 1.51, 95% CI 0.92, 2.49) than mild psoriasis (HR 1.44 95% CI 1.32, 1.57); the confidence interval for the severe psoriasis group, however, spanned a relative risk of 1.0 ().
A statistically significant interaction between psoriasis and sex was found only for depression comparing severe psoriasis patients to controls (interaction term HR 1.21, 95% CI 1.00, 1.46) (). These results suggest that the relative risk of receiving a clinical diagnosis of depression is significantly higher in men compared to women with severe psoriasis. An interaction of psoriasis and age was seen in mild and severe psoriasis groups for all three outcomes with the exception of suicidality in the severe psoriasis cohort, suggesting that the relative risk of these outcomes is greatest in younger patients.
The absolute risk of diagnosis of depression, anxiety, and suicidality attributable to psoriasis (adjusted for age and sex) was 11.8, 8.1, and 0.4 per 1000 person years, respectively (). Attributable risks for these outcomes were similar between mild and severe psoriasis except for depression (11.5 and 25.5 per 1000 person years, respectively). Stated another way, the excess risk attributable to psoriasis is one case of depression for every 39 severe psoriasis patients per year (or per 87 patients per year with mild psoriasis). The excess risks associated with psoriasis for anxiety and suicidality correspond to one case per 123 and 2500 psoriasis patients per year, respectively.
Sensitivity analyses were conducted to ensure capture of incident rather than prevalent depression, anxiety, and suicidality, as well as to test for several types of observation and misclassification. The hazard ratios for the risk of incident depression, anxiety and suicidality remained robust to these sensitivity analyses with the exception of suicidality in the severe psoriasis cohort when patients with prior history of suicidality were excluded from the analysis; these data are included in Appendix A